With the development of technology and the progress of semiconductor manufacturing technique, the size of the internal electronic components in a chip is shrunk to be just dozens of nanometers. Thus, some unexpected sudden voltage or current may cause damage on these tiny-sized electronic components. For example, these electronic components of a chip may be damaged by an electrostatic discharge (ESD) derived from an external pin thereof.
Thus, for all the chip design companies, it is quite important to design a chip capable of preventing from being damaged by an ESD.